If it's setup right (can't see properly), then the middle plate should be locked to the flywheel-pressure plate, like truck twin plate setups are. Basically you double the friction surface.
Yep that's it you can just see the centre plate locking into the flywheel in the bottom of the 1st pic, its made up out of a 2F pressure plate and 2x 2F clutch plates, its a pretty tight fit to get the release bearing in there but it just fits
still cant get my head around all this clutch clamping stuff we put a centreforce clutch in my other cruiser and the guy gave me a dual friction clutch plate with small segmented linings on one side and assured me that would give me better clamping than a standard lining, I guess he's the expert and it definitely clamps up tight but still doesn't sound right that less surface area would give me more clamping
sorry for the thread jack with all my clutch stuff